Device for crucible-free zone melting having sealing means for a sliding member

ABSTRACT

Device for crucible-free zone melting a crystalline rod substantially vertically supported at the ends thereof in a zone melting chamber includes heating means extending into the chamber through a substantially vertical slot formed in a side wall of the chamber. Slide means located adjacent the side wall carries the heating means and is slidable therewith relative to the rod axis. Elastically deformable sealing means are mounted between the sliding surface of the slide means and the side wall and completely surround the slot so as to seal it gas-tightly. The slide means, at least at the sliding surface thereof, are formed of a material of good slidability, the sealing means are formed of a material effecting a dry seal with the sliding surfaces, the paired materials having a frictional coefficient of at most 0.2.

nited States Patent Erneis et a1.

Ebermannstadt; Wolfgang Keller, Pretafeld, all of Germany Siemens Aktiengesellschait, Berlin and Munich, Germany Filed: Jan. 14, 1969 Appl. No; 790,985

Assignee:

Foreign Application Priority Data Jamie, 1968 Germany ..P l7 19 512.9

111.8. Cl..... ..23/273 SP, 49/477 Int. Cl. ..B0lj 17/10, E061) 7/16 Field ofScarch ..23/273, 301; 49/477, 234, 235;

SOS/DIG. 7; 277/3, D10. 6

References Cited UNITED STATES PATENTS 8/1962 Trexler ..49/477 Anderson et al ..49/477 Heneage et a1. ..23/273 [5 7] ABSTRACT Device for crucibie-free zone melting a crystalline rod substantially vertically supported at the ends thereof in a zone melting chamber includes heating means extending into the chamber through a substantially vertical slot formed in a side wall of the chamber. Slide means located adjacent the side wall carries the heating means and is slidable therewith relative to the rod axis. Elastically deformable sealing means are mounted between the sliding surface of the slide means and the side wall and completely surround the slot so as to seal it gasnightly. The slide means, at least at the sliding surface thereof, are formed of a material of good slidability, the seal ing means are formed of a material effecting a dry seal with the sliding surfaces, the paired materials having a frictional coefficient of at most 0.2.

7 Claims, 3 Drawing Figures Patented March 21, 1972 3 Sheets-Sheet l Patented March 21, 1972 3 Sheets-Sheet 3 T0 VACUUM PUMP DEVICE FOR CRUCIBLE-FREE ZONE MELTING HAVING SEALING MEANS FOR A SLIDING MEMBER SPECIFICATION Our invention relates to device for crucible-free floating zone melting of a crystalline rod, especially of semiconductor material and, more particularly, is an improvement over the invention of one of the coinventors of the instant application, W. Keller, disclosed in copending application Ser. No. 669,979, filed Sept. 22, 1967 and assigned to the same assignee as that ofthe instant application.

In the aforementioned copending application there is described a device for crucible-free zone melting a crystalline rod comprising a zone melting chamber having a side wall formed with a substantially vertical slot, heating means extending through the slot into the chamber and energizable for forming a melting zone in a substantially vertically supported crystalline rod mounted in the chamber, slide means located adjacent the side wall and carrying the heating means, the slide means and the heating means being slidable together relative to the rod in the direction of the rod axis whereby the melting zone is passed through the rod, and an elastically deformable sealing strip mounted between the slid means and the side wall ofthe zone melting chamber and completely surrounding the slot whereby the slot is gas-tightly sealed. The sealing strip has, for example, a C-shaped cross section and is forced by a pressurized medium against the sliding surface of the slide means. Oil subjected to a superpressure of 3 to atmospheres excess pressure is employed as the pressurized medium. As the slide means is displaced, however, a relatively thick oil film is formed on the sliding surface of the slide means and vaporizes, thereby impairing the high vacuum in the zone melting chamber.

It is accordingly an object of our invention to provide device for crucible-free floating zone melting of crystalline rods which avoids the foregoing disadvantage and which, more particularly, provides sealing between the slide means and the wall of the zone melting chamber which completely prevents vapor-formation, especially the formation of hydrocarbon vapor.

With the foregoing and other objects in view, we provide device for crucible-free floating zone melting of the aforementioned type wherein the slide means, at least at the sliding surfaces thereof, are formed of a material of good slidability, and the sealing means are formed of a material effecting a dry seal with the sliding surfaces, the paired materials of the sliding surface and the sealing means having acoefficient of friction ofat most 0.2..

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in device for crucible-free floating zone melting a crystalline rod, especially of semiconductor material, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection the accompanying drawings, in which:

FIG. 1 is a diagrammatic elevational view of device for crucible-free zone melting a crystalline rod according to our invention showing a zone melting chamber containing a heating device displaceable in a slide in the axial direction of the rod that is being zone melted;

FIG. 2 is an enlarged perspective view of details of the slide guidance structure shown at the left-hand side of FIG. I; and

FIG. 3 is a cross-sectional view of FIG. 2 taken along the line III-lIl in the direction ofthe arrows.

Referring to the drawings and particularly ,to FIG. 1 thereof, there is shown a zone melting chamber 1 which can either be a vacuum chamber, a protective gas chamber or a high-pressure chamber. A slide guidance structure 3 is secured to one of the vertical walls 2 of the zone melting chamber 1. A slide 4 adjustable in the axial direction of a crystalline rod 27, such as of semiconductor material, which is suitably end-supported by holders 28 of conventional construction in the chamber 1, is guided in a slideway defined by a bearing bed 5 and lateral side walls 6 and 7. A ball roll spindle 9 actuated by a motor 8 is provided as drive means for the slide 4. The heating device includes an inductive heating coil 10 displaceable with the slide 10 and a further heating coil 11 adjustable in a direction perpendicular to the axis of the rod 27 being subjected to the zone melting process.

The ball roll spindle 9 assures virtual vibration or shock-free displacement of the slide 4 in roller bearings 13 to 15 (FIG. 2) that are fixed to the side walls 6 and 7 as well as to the bearing bed 5. An elongated slot 116 through which the heating coils l0 and 11 extend into the chamber 1 is formed in the bearing bed 5, and is surrounded by two elastically deformable sealing members 17 and 18. A guiding device 12 for the displaceable holder 20 of the heating coil 11 is displaceable in the direction of the associated double-headed arrow (FIG. 2) on guide rods 21 and 22. The heating coil 10 is held by a holder 23.

As may be seen in FIG. 3, the upper and lateral roller bearings 13 and 14 are resiliently mounted by means of plate shaped or leaf springs 24 and 25, respectively, whereas the roller bearings 15 located at the bearing bed 5 are rigidly fixed thereto. The slide 4 is provided on the sliding surface thereof with a layer 26 of a material having good slideability, i.e., a low coefficient of friction. The layer 26 must also be heat-resistant and must especially have no tendency to form a gas even when heated up to temperatures of about 200 C. The sealing members 17 and 18 are formed of a material suitable for a dry seal.

The paired materials respectively forming the sliding surface ofthe slider 4, on the one hand, and the sealing elements 17 and 18, on the other hand, have a coefficient of friction of at most 0.2. Plastic materials, ceramic coatings or glazes are suitable materials for producing the layer 26 and therewith the sliding surface of the slide 4. Wear-resistant rubber-elastic materials having a degree of hardness of about to 100 Shore, preferably Shore, are advantageously used as material for the sealing elements 17 and 18.

Especially desirable pairs of materials are tetrafluorethylene as the layer 26 providing the sliding surface of the slide 4, and rubber-elastic materials known by the trade names Viton and Perbunan as material for the sealing elements 17 and 18. Polyurethane is also suitable in addition to Viton," which is formed of copolymers of vinylidenefluoride and hexafluorpropylene, and to Perbunan, which is butadiene-acrylnitrilcaoutchouc.

In the usual case wherein the slide 4 is made of steel, it is desirable to roughen the surface thereof and to produce the polytetrafluorethylene layer by sintering. Depending upon the respective roughness or smoothness of the surface of the slide 4, a thickness of between 10 and 50 ,u of the layer 26 is adequate.

As has been found, it is advantageous in many cases of use, especially when the displacement path of the slide 4 is less than 1 meter, to make the slide 4 itself out of the slideable or low-friction material. For stiffening or reinforcing purposes, a suitable insert, preferably of steel, can be provided. Similarly, the slideway contact surfaces can be reinforced with steel bands.

In order to achieve reliable sealing between the slide 4 and the wall of the zone melting chamber 1, when two or more sealing elements 17 and 18 are used, it is advantageous to connect the space or spaces located between the individual sealing elements 17 and 18 to a prevacuum pump at the inlet 19. For a vacuum of about 10 torr in the zone-melting chamber 1, the prevacuum of the pump may be about 10'] torr.

The displacement speed of the slide 4 is generally between and 30 mm./min.

The provision of a dry seal between the sliding surface of the slide 4 and the sealing members 17 and 18 affords the advantage that no vapor is formed that can penetrate through the slot 16 into the zone melting chamber 1. This is particularly advantageous for high-pressure chambers, because the required vacuum is not affected thereby. Furthermore, the known disadvantage of the oil seals, namely the penetration of hydrocarbon vapor into the zone melting chamber and the introduction of elementary carbon into the crystalline semiconductor rod, is avoided. The inclusion of carbon is especially disturbing in the processing of silicon.

We claim:

1. Device for crucible-free zone melting a crystalline rod comprising a zone melting chamber having a side wall formed with a substantially vertical slot, heating means extending through said slot into said chamber and energizable for forming a melting zone in a substantially vertically supported crystalline rod mounted in said chamber, slide means located adjacent said side wall and carrying said heating means, said slide means and said heating means being slidable together relative to the rod in the direction ofthe rod axis so as to pass the melting zone through the rod, elastically deformable sealing means mounted between a sliding surface of said slide means and said side wall of said melting chamber and completely surrounding said slot, and means for yieldably biasing said slide means toward said sealing means whereby said slot is gas-tightly sealed, said slide means, at least at said sliding surface thereof being formed of a material of good slideability, said sealing means being formed of a material effecting a dry seal with said sliding surfaces, the paired materials of said sliding surface and said sealing elements having a coefficient of friction of at most 0.2.

2. Device according to claim 1, wherein said material of good slideability forming said sliding surface consists of synthetic plastic material.

3. Device according to claim 1 wherein said material of good slideability forming said sliding surface consists of polytetrafluorethylene.

4. Device according to claim 1, wherein said material of said sealing means consists of a copolymer of vinylidene fluoride and hexafluorpropylene.

5. Device according to claim 1, wherein said material ofsaid sealing means consists of polyurethane.

6. Device according to claim 1, wherein said sealing means comprises a pair of sealing elements surrounding said slot and radially spaced from one another so as to define a space therebetween, and means communicating with said space for forming a prevacuum therein.

7. Device according to claim 6, wherein said prevacuum forming means is a prevacuum pump. 

2. Device according to claim 1, wherein said material of good slideability forming said sliding surface consists of synthetic plastIc material.
 3. Device according to claim 1 wherein said material of good slideability forming said sliding surface consists of polytetrafluorethylene.
 4. Device according to claim 1, wherein said material of said sealing means consists of a copolymer of vinylidene fluoride and hexafluorpropylene.
 5. Device according to claim 1, wherein said material of said sealing means consists of polyurethane.
 6. Device according to claim 1, wherein said sealing means comprises a pair of sealing elements surrounding said slot and radially spaced from one another so as to define a space therebetween, and means communicating with said space for forming a prevacuum therein.
 7. Device according to claim 6, wherein said prevacuum forming means is a prevacuum pump. 